Penetrators for armor piercing shells have in the past been prepared from materials that have the desired strength and density to penetrate armor.
A more desirable material would not only have the density and strength to penetrate the armor, but also be capable of being broken into pieces of an intermediate size. If the material is too strong then either no particles or a small number will be formed thus creating only local damage. If, however, the material breaks into very fine particles, the resulting particles will not penetrate and do little or no damage.
Some materials in the past have been tungsten alloys with minor amounts of iron, nickel or copper. While these materials have the strength and density to allow penetration of armour when fired from a conventional weapon such as an anti-tank gun, they do not possess the desired frangibility characteristics to enable them to break apart upon impact to form particles in the desired size range.
It is believed, therefore, a material having a sufficient strength and hardness to enable penetration of light armour and with a desired amount of frangibility to enable the material to fragment in a desirable manner would be an advancement in the art.